Most of us spend our days on our behinds — and it’s killing us

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When you sit for an extended period of time, your circulation slows and you burn fewer calories. Key flab-burning enzymes responsible for breaking down triglycerides (a type of fat) simply start switching off.

You might not want to take the following stat sitting down: According to a poll of nearly 6,300 people by the Institute for Medicine and Public Health, it's likely that you spend a stunning 56 hours a week planted like a geranium — staring at your computer screen, working the steering wheel, or collapsed in a heap in front of your high-def TV. And it turns out women may be more sedentary than men, since they tend to play fewer sports and hold less active jobs.

Even if you think you have an energetic lifestyle, sitting is how most of us spend a good part of our day. And it's killing us — literally — by way of obesity, heart disease, and diabetes. All this downtime is so unhealthy that it's given birth to a new area of medical study called inactivity physiology, which explores the effects of our increasingly butt-bound, tech-driven lives, as well as a deadly new epidemic researchers have dubbed "sitting disease."

The modern-day desk sentence
"Our bodies have evolved over millions of years to do one thing: move," says James Levine, M.D., Ph.D., of the Mayo Clinic in Rochester, Minn., and author of "Move a Little, Lose a Lot." "As human beings, we evolved to stand upright. For thousands of generations, our environment demanded nearly constant physical activity."

But thanks to technological advances, the Internet, and an increasingly longer work week, that environment has disappeared. "Electronic living has all but sapped every flicker of activity from our daily lives," Levine says. You can shop, pay bills, make a living, and with Twitter and Facebook, even catch up with friends without so much as standing up. And the consequences of all that easy living are profound.

When you sit for an extended period of time, your body starts to shut down at the metabolic level, says Marc Hamilton, Ph.D., associate professor of biomedical sciences at the University of Missouri. When muscles — especially the big ones meant for movement, like those in your legs — are immobile, your circulation slows and you burn fewer calories. Key flab-burning enzymes responsible for breaking down triglycerides (a type of fat) simply start switching off. Sit for a full day and those fat burners plummet by 50 percent, Levine says.

That's not all. The less you move, the less blood sugar your body uses; research shows that for every two hours spent on your backside per day, your chance of contracting diabetes goes up by 7 percent. Your risk for heart disease goes up, too, because enzymes that keep blood fats in check are inactive. You're also more prone to depression: With less blood flow, fewer feel-good hormones are circulating to your brain.

Spending the day on your rear is also hell on your posture and spine health, says Douglas Lentz, a certified strength and conditioning specialist and the director of fitness and wellness for Summit Health in Chambersburg, Pa. "When you sit all day, your hip flexors and hamstrings shorten and tighten, while the muscles that support your spine become weak and stiff," he says. It's no wonder that the incidence of chronic lower-back pain among women has increased threefold since the early 1990s.

And even if you exercise, you're not immune. Consider this: We've become so sedentary that 30 minutes a day at the gym may not do enough to counteract the detrimental effects of eight, nine, or 10 hours of sitting, says Genevieve Healy, Ph.D., a research fellow at the Cancer Prevention Research Centre of the University of Queensland in Australia. That's one big reason so many women still struggle with weight, blood sugar, and cholesterol woes despite keeping consistent workout routines.

In a recent study, Healy and her colleagues found that regardless of how much moderate to vigorous exercise participants did, those who took more breaks from sitting throughout the day had slimmer waists, lower BMIs (body mass indexes), and healthier blood fat and blood sugar levels than those who sat the most. In an extensive study of 17,000 people, Canadian researchers drew an even more succinct conclusion: The longer you spend sitting each day, the more likely you are to die an early death — no matter how fit you are.

The non-exercise answer
So if exercise alone isn't the solution, what is? Fortunately, it's easier than you think to ward off the perils of prolonged parking. Just ramp up your daily non-exercise activity thermogenesis — or NEAT. That's the energy (i.e., calories) you burn doing everything but exercise. It's having sex, folding laundry, tapping your toes, and simply standing up. And it can be the difference between wearing a sarong or flaunting your bikini on your next beach vacation.

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In his groundbreaking study on NEAT, the Mayo Clinic's Levine used motion-sensing underwear (hot, huh?) to track every single step and fidget of 20 people who weren't regular exercisers (half of them were obese; half were not). After 10 days, he found that the lean participants moved an average of 150 minutes more per day than the overweight people did — enough to burn 350 calories, or about one cheeseburger.

Fidgeting, standing, and puttering may even keep you off medications and out of the doctor's office. Think of your body as a computer: As long as you're moving the mouse and tapping the keys, all systems are go. But let it idle for a few minutes, and the machine goes into power-conservation mode. Your body is meant to be active, so when you sit and do nothing for too long, it shuts down and burns less energy. Getting consistent activity throughout the day keeps your metabolism humming along in high gear.

When you get out of your chair and start moving around, you turn on fat burners. Simply standing up fries three times as many calories as sitting on your butt, according to Levine. And, he adds, "NEAT activity can improve blood flow and increase the amount of serotonin available to the brain, so that your thinking becomes sharper and you'll be less likely to feel depressed."

Get your move onShake things up throughout the day by interrupting your sedentary stints as often as possible. "Stand up every half hour," says Neville Owen, Ph.D., of the University of Queensland. "If you have to sit for longer than that, take more extended and active breaks and move around for a few minutes before sitting back down."

When you're reading e-mail and taking phone calls, do it standing. Walk with colleagues to brainstorm ideas. And consider trading your chair for a large stability ball. "It forces you to engage your muscles, and you're likely to stand up more because you're not melting into a chair," Lentz says.

At home, it's simple: Limit TV time to two hours a day or less. Better yet, watch it from a treadmill or exercise bike. Among women, the risk for metabolic syndrome — a constellation of health woes including high blood pressure, high cholesterol, and high blood sugar — shoots up 26 percent for every hour per day they spend watching the tube.

Not sure how much of a difference these mini moves will make? Swapping a more active approach for just a few of your daily activities can help stave off the one-to two-pound weight gain most women accumulate every year — and it can keep your metabolism buzzing the way nature intended it to.